Method of reducing and converting metals and making alloys



Patented Apr. .26, 1932 PERCY A E. ARMSTRONG, OF NEW YORK, '11. Y.

METHOD OF REDUCING AND CONVERTING METALS AND MAKING- ALLOYS No Drawing.Application filed July 29,

The present invention relates tova process for the production of metalsand alloys low in carbon and which may be produced low in silicon oraluminum, or with a definitely controlled amount of silicon or aluminumin- .5 cluded. The process is particularly adapted to the treatment ofthe high melting point metals used as alloying ingredients, such aschromium, vanadium, zirconium, titanium,

w tantalum and uranium.

In the manufacture of alloy steels or of high melting point alloys,- itis usual to melt down the main ingredient such for example as iron ornickel and add to the refined main ingredient a fe'rro-alloy of thealloying metal. Where nickel is the main ingredient, the use of theferro compound may add an undesir-.

able iron content to the finished product and therefore in such a casethe alloy may be added as a pure metal.

In some cases, particularly where iron is the main ingredient, the alloyis added in the form of an oxid which is mixedwith the charge of ironand melted down together 85 with a reducing agent. If this is done, the

accurate composition of the final product is,

obtained by adding corrective amounts of the ferro-alloy-to the meltafter an analysis has been made andbefore pouring. As anotheralternative, the basic metal is melted and then an oxid of thealloying'metal mixed with a reducing agent is thrown on the slaggedsurface of the molten metal. So much of the alloying metal as is reducedwill sink down into the metal of the bath. This latter process is notentirely satisfactory, for it is almost always, attendant by largewaste, inasmuch as the oxide of the alloying metal is seldom, ifever,entirely reduced,

@ for example, in the case where one seeks to alloy chromium with ironby adding chromite and a reducing agent to the slag covering the bath ofmolten iron, only from about to 70% of the chromite is reduced and so asmuch reducing agent has to be used, that the reducing agent is carriedinto the finished product in undesirable quantities. It will also befound that the bath is highly gasified, or wild, and the slag tends togrow to such w proportions that it cannot be handled, and a 1927. SerialN0. 209,395.

great amount of heat is wasted keeping the slag fluid. For example,chromite has a metallic chromium content of about 33 and an iron contentof about 14% so that even if all of the metal is reduced the amount ofslag will be greater than the amount of metal. Inasmuch as chromite isvery refractory and difficult to fuse it will also be found that thereaction will be slow and'will demand a very high temperature which willtend to cause the furnace lining to be cut and damaged.

Even where a ferro-alloy is used the process is a slow and expensiveone; for example, if ferro-chromium containing about of chromium withlow carbon is thrown on the 65 surface of molten iron in suflicientquantity required in a 5-ton melt of a 15% chromium alloy, from 1% to2,hours will be needed to melt the ferro-chromium. vSuch alloys are iusually made in an electric furnace and. such a bath as described willpick upat least .05% of carbon for each 30 minutes that the arcs are on,so that if one starts with a practically carbon-free iron, the resultingprod; uctwill have in excess of from 1570 to 20% carbon, Whereas, insuch an alloy it is usually desirable to keep the carbon content below I.10%. In the same way, when metallic chromium is added to nickel in themanufacture of an alloy such as one containing nickel and 25% chromium,it will be found thatthe metallic chromium is diflicult to fuse as wellas being very expensive, and if the alloy. is formed in an electricfurnace the carbon. content will be raised, which is extremelyundesirable.

By my invention I have evolveda process whereby these high melting pointmetals may readily be obtained in a form adapted for use in makingalloys, which isbased upon the discovery that the fluorine compounds ofthese metals can be reduced with extraordinary ease, and that if theoxides are mixed with a substance adapted to generate fluorine atreducing temperatures there appears to be some interaction of thefluorine with the oxide which permits the oxide to be readily reduced.The fluorine compound used may be one of which the resulting stableingredients will go OK with the slag or will enter into the metalproduct such for example as a fluoride of the metal to be reduced or ofsome other high melting point metal or a double fluoride of such ametal, or a some- 5 what difl'erent type of fluoride such as sodiumfluoride. It is also advisable to have a reduclng agent such as siliconor aluminum present (which appears to combine with some of the fluorine)and I also find it advantageous to incorporate some lime in the mixturewhich appears to take up excess fluorine, forming fluorspar which keepsthe slag fluid,

also helping to prevent the escape of fluorine which would tend topoison the atmosphere.

Thus far my researches have shown only the empirical results, and I amunable to give any satisfactory explanation of what transpires, butapparently the fluorine acts in the nature of a catalyst to aid in thereduction of the oxide.

In any event, the fluorine compounds (such for example as chromiumfluoride) act in a very different matter from the oxides or any othercompound with which I have Worked, for instead of the reduction beingslow and only partial, it is almost instantaneous and is complete. Wherethe metal is in whole or in part in the form of the oxide mixed with Ithe fluorine compound (which may be a compound of the same metal or someother compound) the reduction is somewhat less rapid, but still isquantitative provided sufiicient fluorine is present, as for example inthe case of a mixture comprising approximately three parts by weightofchromite and 1 part of chromic fluoride. This relationship is one whichI have found satisfactory but is not given as establishing a limit.

As regards the reducing agent, I find that silicon is somewhat moreeflicient than aluminum. This is apparently due to the fact that siliconand fluorine combine to form a gas which in turn may react on the oxide.In either case, the amount of reducing substance thatyneed be used canbe calculated, so that there will not be a residue to go over intothe-resulting product.

7 The compounds of the metal to be reduced are preferably finely groundand mixed with the reducing'agent and with lime and then thrown on a hotslag which may cover a melted metal such as iron with which the highmelting point metal is to be alloyed, or may cover a bath of the metalwhich is being reduced or a ferro compound thereof. The reduced metalwill trickle through the slag into the bath and will not be reoxidizedby the air. I

For carrying on the process, the furnace should be lined with arefractory material that is not readily acted upon by fluorine. I find alining of magnesite and a roof of chromite can be used, whereas, ifsilica brick or fire brick is used for the lining, they will 5 melt awayvery rapidly.

My invention enables me to make chromium alloys with iron or nickelbases such as rustless iron or steel or alloys of the well knownnichrome type at a very low cost.

Alloys containing zirconium have heretofore been very difficult toproduce and as far as I know it has never been possible to produce aferro-zirconium having a low silicon content. Zirconium is a valuablealloy in steel, but its use remains undeveloped due tothe-fact that ithas always been accompanied by silicon which has befogged andcomplicated the true effects of the zirconium in iron.

Tantalum is a very excellent alloying steel but heretofore one could notalloy it with steel without great loss due to oxidation, and theentrapped oxides caused the alloy to be so dirty that the good effectsof the tantalum were obscured by mechanical defects.

Titanium also is diflicult to get into steel in any but smallproportions, because ferrotitanium thrown on the surface oxidizesreadily. The carbide is useless for anything except as a degasifier.

Uranium is a very useful element in steel but very difficult toincorporate because it oxidizes so readily.

Vanadium is used to a considerable extent in making ferrous alloys, butits use has been restricted due to the high cost of ferro-vanadium. Bymy process the vanadium and the other alloying metals referred to can beincorporated into the bath without difliculty. For example, in the caseof vanadium, the simple fluoride VF may be used, whereas, 1n otherinstances such as with tantalum or titanium, it may be found moreconvenient to use a double fluoride.

For the purposes scribe my process as applied to the use of chromium,but it is to be understood that the same procedure may be applied toother high melting point metals such as are used for making alloys.

In the manufacture of an alloy of. the Inchrome type containing forexample nickel and 25% chromium, the nickel is first melted down,preferably in an electric furnace. Sufficient slag is used to protectthe metal from oxidation and the molten mass of illustration I will de-III is degasified by the usual methods. Ordinarily it will not benecessary 'to replace the original slag.

The required amount of chromium fluoride (see examples below) is mixedwith lime, and if desired, a small amount of aluminum or silicon can beincluded. These materials are thoroughly mixed together and then As soonas all action stops, the furnace can be tilted and the heat poured. Theamount of aluminum or silicon used must be kept low unless it is desiredto have one of these substances in the finished alloy. The following areillustrative proportions which I have used successfully:

Example I.Nickel 80 ounces, CrF 51 ounces, lime 24 ounces, aluminum, 3ounces.

The weight of the poured ingot was 106 ounces which on analysis showed75% nickel and 25% chromium, the conversion of the chromium fluoridehaving been complete.

Example .Z.A similar run, but omitting 15 the aluminum, was found togive substantially identical results.

Example 3.-Nickel 80 ounces, CrF 51 ounces, lime 24 ounces, silicon 8ounces.

The weight of the poured ingot was 110 t-ounces and showed the followinganalysis: Nickel 71.45%, chromium 24.9%, silicon 3.65%.

Here, as before, the chromium conversion was complete. I

In the manufacture of rustless heat and acid resisting, orstable'surface iron or steel there are two procedures which can beconveniently followed: In one case the chromium is all added as chromiumfluoride, whereas, g y in th'e'other case the combination of chromiumfluoride and chromite is used- In either --.case I find carbon is not anadvantageous rej d'ucing agent to use, for it is slow and waste fu'l andtends to raise the carbon content of 5;the melt.

The use'of chromium fluoride alone may be illustrated by the case of theproduction of an iron alloy containing 15 or more percentof chromium:The iron is melted down in an m electric furnace and the carbon isremoved by the-use of mill scale or iron ore. The slag is removed andreplaced by a clean lime slag. The bath is degasified withingot-aluminum held under the metal and by shot aluminum 5 on the slag.To the above slag which will con tain calcium oxide together with somealuminum oxide, I add the chromium fluoride mixture prepared similarlyto the examples previously described, or as shown by the fol lowingexamples Example 4.Iron 80 ounces, CrF 24 ounces, lime 12- ounces.

The reduction of'chromium was complete and the slag produced was verywhite. The

total procedure occupied but a very short time. The iron was melted inan electric furnace of the arc type in 15 minutes, degasified in 5minutes, using 2 ounces of aluminum as shot on the slag, and the mixtureof chromium fluoride and other ingredients was added to the surface ofthe molten metal slag in 2 minutes. The mixture fused practically assoon as it was thrown on but the mass was allowed to stand for 5 minutesbefore pouring. The

55 ingot weighed 98 ounces and due to the lime 8 ounces,

in the previous example.

amount of aluminum that was employed,a substantial amount was found inthe product as shown by the following analysis: chromium 12.35%,aluminum 5.6%, carbon .02%, iron balance.

Another test melt comprised the following Eazample 5.Iron ounces, CrF 8ounces,

aluminum 2 ounces. The ingredients were handled exactly as The pouredingot weighed 84 ounces and showed an approximate analysis of: chromium4.76%, aluminum 0%, carbon .01%, iron balance.

In this case it is to be noted that no aluminum went into the finishedproduct but the conversion of chromium was complete. By increasing theamount of chromium fluoride used, the percentage of chromium may beincreased to any desired point, so that if the melted metal inthe'bathis fused chromium, substantially chromium can be obtained. i

If an addition of zirconium, vanadium, tantalum, titanium, uranium orthe like is required, a fluoride or double fluoride of such metal can bemixed with the chromium fluoride and the conversion can be conducted insubstantially the same way; or these materials canbe used alone or mixedtogether without the useof any chromiumfluoride.

The examples are set forth in terms of small (}uantities which wereusedfor the purpose o simplifying measurements and analyses; but myexperience has shown th atv substantially the same conditions will holdgood for large batches. I I

I have described these examples as conducted in the electricarc typeoffurnace but other types of furnace can be used and the process isparticularly adapted'to ope-n hearth practice. It is to be understoodthat the ingradients added to the slag can be preheated if desired to apoint below that at which fluorine is liberated and if desired powderedadditions can be briquetted to facilitate handling.

Where fluoride and oxide are used together and where it is desired tokeep the silicon or aluminum content very low, the theoretical amount ofsilicon or aluminum-to be used mag be calculated as follows pproximatelyone-fifth as much silicon or aluminum or both should be used to takecare of the chromium fluoride, while 18% of the weight of chromite insilicon or 21% of.

the weight of chromite in aluminum should also be included.

When a fluoride (of the metal or some other fluoride) is used inconjunction with the metallic oxide, it is apparent that the fluorinehas some eflect on the oxide, for the reduction of the oxide will takeplace with great rapidity and can be completed with only. thetheoretical amount of reducing agent present. The following are examplesof the combined use of chromium fluoride and chromite:

E xample 6.-1'ron 80 ounces, CrF 16 ounces, chromite 48 ounces, lime 12ounces, 80% ferrosilicon 12 ounces.

The iron was melted down in 15 minutes. The melt was degasifled with oneounce of shot aluminum thrown on the lime slag. A mixture of powderedchromium fluoride, chromite, lime and ferro-silicon which had previouslybeen well mixed, was thrown on the slag with the are turned on. It took6 minutes to make this addition but the mixture fused almost as quicklyas it was added.

The heat was allowed to stand with the are on for ten minutes, thoughthe action appeared to end in about five minutes after the last additionwas made. The heat was poured and the ingot resulting weighed 110ounces, which was the full theoretical weight. The chromite was found tobe entirely reduced and the chromium fluoride to be entirely converted.The approximate analysis of this heat was: chromium 24.20%, carbon .01%,iron balance.

A similar heat was made using aluminum in place of silicon withidentical results being obtained, though the action was not quite asrapid.

In another case a run was made to check up the accuracy of the process.The ingredients used were as follows:

Example '/".Iron 80 ounces, CrF 6 ounces, chromite 16 ounces, lime 6ounces, 80% ferrosilicon 7 ounces.

If one disregards the excess silicon, the theoretical weight of thefinished ingot will be 93 ounces' However, it can be calculated thatthere has been used a. theoretical excess of silicon approximating 1.5ounces. When the heat was finished and poured it was found, that thefinished ingot weighed 94.5 ounces, giving exactly the theoreticalresults. The approximate analysis of the ingot was: chromium 8.7 5%,silicon 5.25%, carbon .01%, iron balance.

If one desires to make ferro-chromium instead of producing the alloydirectly, this can be done either by converting chromium fluoride in alarge quantity over a' bath containing a relatively small amount of ironor the chromite and chromium fluoride can be treated jointly, as shownby the following.

example: I

Example 8.-Tron 4 ounces, CrF 48. ounces, chromite 144 ounces, lime 24ounces, 80% ferro-silicon 48 ounces; (Fe 9.6 ounces).

This composition gave an ingot weighing 105 ounces (which is almostexactly the theoretical weight) containing approximately chromium and30% iron.

For the manufacture of ferro-chromium I prefer to use a multipleelectrode arc furnace having a roof instead of the open type arcfurnace. However, in View of the speed of the reaction and theextremely. liquid type of slag an electric type are furnace of thereducing type can be used or an open hearth furnace can be employed,particularly when the chromium ingredients are preheated.

Heats made by my process can have any desired ferro alloys added to themor the initial bath may be rich in one or more of the elements. While Iprefer to use an initial bath which will prevent the high melting pointmetal from becoming oxidized, it may be possible to omit this undercertain conditions.

"While the foregoing examples are restricted to chromium and to chromiumcompounds of fluorine, it is to be understood that they are equallyapplicable to other high melting point alloying metals, though of coursesome difference in relative amounts of ingredients might have to be made(due to differences in valences, molecular Weights and the like) asanyone skilled in the art will readily understand. Also in place of thefluorine compound of the metal other fluorine compounds such for exampleas sodium fluoride can be used to supply fluorine to react with theoxide. Such fluorine compound should be one which will decompose at orbelow the melting point of the metal but will not decomposeatrelatively-low temperatures, as otherwise the fluorine may escape as agas before the metallic compound reaches thereducing temperature.

What I claim is:

1. The process of reducing a compound of a high melting point metal ofthe type used in making ferrous alloys, which comprises the step ofthrowing on a hot fused slag a mass comprising a fluorine compound ofsuch metal.

2. The'process ofv reducinga compound of a high melting point metal ofthe type'used in making ferrous alloys which comprises the step ofthrowing on a hot melted slag a mixture comprising an oxide of such ametal, a fluorine compound of such a metal and a reducing agent.

3. The process of producing ferrous alloys which comprises the step offorming a bath of molten ferrous metal with a slag onthe surface andadding to such slag a finely divided mass comprising a fluorine compoundface and adding to such slag a mass comprising chromite, chromiumfluoride and a -reducing agent.

ERCY A. E. ARMSTRONG.

